1. Field of the Invention
The invention concerns a device to support the head of a patient accommodated on a patient bed of an x-ray apparatus.
2. Description of the Prior Art
Conventionally, a head shell that can be affixed to the patient is provided for medical examination of the head, for example by means of x-ray computed tomography. To prevent artifacts in the head image, the head shell is produced from a material permeable for x-rays, for example fiber-reinforced plastic. To adjust the necessary examination position of the head, the angle of inclination of the head shell can be adjusted relative to the patient bed. For this purpose, the head shell is connected with the patient bed via a hinge executed such that it can be locked by a clamping screw. A leg of the hinge is connected with a fastening part to fasten the device to the patient bed. Substantial material thicknesses are required in order to ensure a sufficient stability of the hinge (likewise produced from a material permeable for x-rays). In practice, such a hinge causes image artifacts.
To minimize or prevent such artifacts one known approach, using asymmetrical configuration, is to arrange the hinge as far as possible outside the region of the head to be examined. The head shell is connected, for example, with the patient bed via a laterally mounted arm fashioned in the form of a half-arc, the hinge being a component of the arm. The occurrence of artifacts still can not be completely prevented with this relatively elaborate design. As before, it is necessary to eliminate such artifacts by means of complicated calculational correction methods on the image data after the implementation of a measurement (scan).
DE 297 06 436 U1 discloses a skull supporting device for a patient bed of a computed tomography system. An adapter part that can be attached on the patient bed is provided. A skull support is fastened on a carrier and held on the adapter part on one side by this carrier by means of a carrier arm, and can be pivoted around a horizontal axis. Locking of the skull support is possible by means of a blocking key that engages teeth on the adapter part. The blocking key can transfer the hinge mechanical moment (torque) that occurs upon loading of the skull support to a support part that is affixed on the underside of the carrier of the skull support. The forces arising from the weight of the head are conducted onto the pivotable hinge between the adapter part and carrier arm via the support part and the blocking key. The pivotable hinge must be able to operate under significant mechanical load and therefore must be ruggedly designed, thus requiring relatively massive parts. In tomographical acquisitions in which the x-ray source and detector rotate around the head of the patient, the pivotable connection is located in the beam path and can cause artifacts due to radiation absorption or radiation deflection.
A device for retention of the head in skull surgery is known from DE 40 40 789 A1. The device has a support for the back of the head to support the head of a patient lying on his or her back. With a first part and a second part of a mount, the support for the back of the head is connected with a patient support table by a clampable swivel joint. The swivel joint can be clamped to change the position of the head of the patient. The swivel joint and its clamping device accordingly bear the entire weight of the head and the device for retention of the head. The swivel joint therefore must be fashioned with a high mechanical stability. Low material thicknesses thus cannot be realized. In order to prevent artifacts in the computed tomography image, it is proposed to use polymethylacrylate for many parts of the retention device, but an aluminum alloy is used for the swivel joint. This is not permeable to x-rays. So as to generate as few artifacts as possible in the tomographic image, the hinge is arranged outside of the region of the head to be examined. This means that cantilever forces acting on the swivel joint are even larger and the design is thereby even more elaborate.
A device for supporting a patient in an x-ray examination is known from DE 698 21 368 T2. A tiltable headrest is provided that is connected via a connection piece with a retention plate for supporting the upper body of the patient. A pivotable joint is provided between the connection piece and the headrest. The joint must accommodate forces arising due to the weight of the head. From FIG. 8 it is clear that the joint has teeth and can be clamped. In order to withstand the loads, the joint must be massively designed. The problem of artifact formation is addressed by the joint being arranged above the region of the head to be examined. Nevertheless, artifacts cannot be precluded.